The present invention is related to a foam dispensing gun which dispenses a settable urethane foam made from two components which react with each other to form the foam, and, in particular, to such a gun which will dispense the two components in substantially a 1:1 ratio .+-.5%, in which the two components are not mixed until they reach the exit nozzle, and in which the flow of the resins through the gun can be more easily controlled.
The foam dispensing technology is based on dispensing two liquid resin components, A and B, with a manually operated apparatus which keeps the two components separate until they reach a mixing area. As is known, once the two components are combined in the mixing area, the components react with each other to produce a quickly curing urethane foam. Prior devices include numerous configurations for activation of the trigger, various valve concepts and different discharge characteristics. Examples of the prior devices are shown in U.S. Pat. No. 4,913,317 to Wemicke, U.S. Pat. No. 5,158,233 to Foster et al., U.S. Pat. No. 5,219,097 to Huber et al., U.S. Pat. No. 5,246,143 to Cherfane, U.S. Pat. No. 5,265,761 to Brown, U.S. Pat. No. 5,271,537 to Johnson, and U.S. Pat. No. 5,462,204 to Finn. There are numerous variations of the types of foam dispensing guns described in these patents, however all such variations have drawbacks to a greater or lesser degree that have not been fully resolved.
Some of the problems can best be seen in the foam gun disclosed by Finn, U.S. Pat. No. 5,462,204. Some of the disadvantages of the Finn design are due to the two movable needles employed by the design. The two needles need separate springs and seals. Further, there are two sets of seals for each needle to prevent the components from entering the chamber which receives the arms of the trigger which move the needles. If resins enter this area, or if contaminates get into this area, the foam gun can be rendered useless. The formation of two separate high pressure chambers, one at the front and another at the back of the movable needles, increases the chances for seal failure due to contamination. Another disadvantage is due to a passage geometry which restricts or impedes the flow of materials through the gun. The flow path followed by the material changes direction twice which reduces material velocity through the gun. Yet another problem of this type of passage geometry is that resin or foam, which is not fully dissolved, will accumulate in the passageway. This collection of contaminants in the passageway can cause premature closure of the passageway. This can obviously adversely affect the function of the gun.
Another problem is created by the ability of foreign matter to enter the passageways through the trigger receiving chamber in the middle section of the needles. This chamber is designed to be open to the outside to engage a trigger. Thus the seals are exposed, and contaminates can easily collect in the chamber. Contaminates may also be brought into the rear high pressure chamber by movement of the needle. This area may have a residual coating of the resin. The accumulation of materials is also possible due to the fact that each of materials "A" and "B" will harden over time when they are exposed to an open atmospheric conditions. The presence of moisture will accelerate material hardening.